Tuesday, June 2, 2015

In the second installment of our
updates on the status of the Hawaiian land snail fauna we are covering the two
most species rich families represented in Hawaii, the Amastridae (Figure 1A-E)
and Achatinellidae (Figure1F-J). Both families belong to the informal group
Orthurethra within the Stylommatophora (Bouchet and Rocroi 2005), and together
represent 71% of the recognized Hawaiian land snail diversity. The
Achatinellidae, specifically species within the subfamily Achatinellinae, are
probably among the more well-known of the two owing to the fact that all 41
species of the genus Achatinella were
listed as endangered under the United States Endangered Species Act (ESA) in
1981 and have received considerable attention and conservation funding since. Recently,
several species from other genera within the Achatinellinae were listed as
Candidate Species, but no other Hawaiian land snail species are officially recognized
as endangered or threatened by either the IUCN or the United States Fish and
Wildlife Service. Part of the efforts of our ongoing research is to bring the
plight of the remaining snail fauna to light, so what is left may be saved.

The Amastridae are less well known despite being the only extant family
of plants or animals endemic to the Hawaiian Islands, and being the largest
family of Hawaiian land snails in terms of numbers of species and size. Currently,
none of the Amastridae are protected under the ESA, and only 33 are listed as
extinct on the IUCN Red List (Régnier et al. in press). But like the Achatinellidae
they have suffered from extraordinary rates of extinction, but have yet to
receive the considerable funding or research attention needed to protect them.
Solem (1990) and others (e.g. Zimmerman 1948) emphasized that endemism at the
family and subfamily levels among the Hawaiian snail fauna notably set them
apart from all other native Hawaiian animal groups. Not even the extraordinary
radiation of terrestrial arthropods can lay claim to endemism at this level. There
were 325 amastrid species belonging to eight genera divided into two
subfamilies, the Amastrinae (Figure 1 A-D) and Leptachatininae (Figure 1E), although
more than 85% of the species are in either the genus Amastra or Leptachatina
(Cowie et al. 1995). The family also includes the largest of all Hawaiian land
snails, Careliaturricula, which reached 80 mm in shell height (Figure 1D).
Unfortunately, Careliaturricula and more than 95% of its kin,
such as the smallest T. rex (Tropidoptera rex; Figure 1C), are now thought
extinct (Régnier et al. in press). While our surveys revealed some surprises,
like finding two species on Kauai (Figure 1E) and one on Maui that were thought
extinct, our assessment of the Amastridae has only confirmed the dire
predictions by most. However, in the shadow of such gloomy results, there is
hope, which comes in the form of Chung’s (1986) and colleague’s successful captive
rearing efforts of several species of amastrids, some no longer found in the
wild. While these efforts have not been undertaken at the scale or with the
rigor needed to recover wild populations, they do offer the possibility of one
day doing so if sufficient long term funding can be secured.

The second most diverse Hawaiian land snail family, the
Achatinellidae, comprising 324 species across the Pacific, with 64% (209) of
these in the Hawaiian Islands, and three species on islands in the Indian Ocean
(Cooke & Kondo 1960, Cowie et al. 1995). The Five of the seven subfamilies
(Pacificellinae, Tornatellininae, Tornatellidinae, Tekoulininae, Elasmatininae;
Bouchet et al. 2005) are distributed across the range, with the latter two
endemic primarily to French Polynesia and the Cook Islands. The other two
subfamilies (Achatinellinae, Auriculellinae; Figure 1F and G) are endemic to
Hawaii (Cooke & Kondo 1960, Cowie et al. 1995), and Pacificellinae,
Tornatellidinae and Tornatellininae (Figure 1H-J) are also represented in
Hawaii. All but one Hawaiian achatinellid species are endemic (Cowie et al.
1995). Of notable significance, is that the biogeographical and morphological
patterns of this family have contributed significantly to the development of
evolutionary theory, particularly fundamental ideas related to the founder
effect, genetic drift and speciation (Gulick 1905, Carson 1987). Unfortunately,
most opportunities to continue such studies with this fauna have been lost to
extinction, but not all.

The charismatic Achatinellinae
(Figure 1E) have received far more conservation-focused research and attention
than other native Hawaiian land snails, including other achatinellids (Figure
1G-J), and their remains significant opportunities to study and conserve the
remaining 10 species, most of which are in captivity. However, because of their
protected status and the substantial resources already dedicated to their
conservation, our work has focused primarily on the other four subfamilies in
Hawaii, for which we estimate at least 40% of the known diversity may be
extinct. Like the Amastridae, our recent survey work suggest that we have
indeed lost a great deal of this once diverse family, but there also remains
glimmers of hope. For example, we recently rediscovered a species, Auriculella pulchra, which many had
thought extinct or at least extirpated from most of its range (Yeung et al.
2015). Similarly, we have found several cryptic species that await description (e.g.
Figure 1J, Elasmias sp.) and a few
species that seem to be locally abundant (e.g. Auriculella uniplicata Figure 2 in Puu Kukui Watershed, Maui,
Hawaii).

Figure 2: Auriculella
uniplicata gathered from a single location on Maui to show the high
abundance of this species and the diversity of shell color patterns. More than
50 individuals of this species were counted from a 10x10 m area in less than 30
min.

About Me

I am the Chair of the Department of Biology and Chemistry at Morehead State University and have been studying the systematic relationships of freshwater mollusks for over 20 years. I am currently managing the American Malacological Society's Molluscan Musings which features various topics on systematics and biodiversity of mollusks. I will be contributing and coordinating activity on these blogs including inviting guest contributors. Thanks for checking it out.